Oligomerized .alpha.-olefins have been known for many years to be effective synthetic lubricating oils. Hamilton, U.S. Pat. No. 3,149,178, describes oligomers of C.sub.6-12 .alpha.-olefins made using a Friedel-Crafts catalyst, a peroxide catalyst or thermal treatment. Hamilton teaches that dimers are unsuitable and it is necessary to remove dimers from the composition in order to avoid having a hydrogenated product with an excessively high pour point. For example, the pour point of an .alpha.-decene oligomer containing dimer made using a peroxide catalyst increased from less than -65.degree. C. to +35.degree. C. upon hydrogenation.
Smith et al, U.S. Pat. No. 3,682,823, teach a method of avoiding the above catastrophic increase in pour point without the necessity of removing dimer by using an alkali metal tetrahaloalanate.
Brennan, U.S. Pat. No. 3,742,082, discloses a process for dimerizing C.sub.6-10 .alpha.-olefins using a boron trifluoride catalyst promoted with phosphoric acid or water. The hydrogenated products are useful as fluid lubricants for industrial applications. The reported products have a 210.degree. F. viscosity of 2.01-2.07 cs, making them too fluid for use in engine crankcase lubricating oil. For example, the lowest lubricating oil grade is SAE 5W which has a viscosity at 100.degree. C. of 3.8 cs minimum (SAE handbook).